(1) Field of the Invention
The present invention relates to a method for detecting prostate cells. More specifically, this invention relates to a method for detecting circulating prostate cells using a nested multiplex reverse transcriptase polymerase chain reaction assay.
(2) The Prior Art
Adenocarcinoma of the prostate is the most common internal cancer in males with an estimated 244,000 new cases per year and 38,000 deaths. (P. A. Wingo, et al., Ca. Cancer J. Clin. 45: 8-30 (1995)). The diagnostic tools of serum prostate-specific antigen (PSA) level, digital rectal exam, transrectal prostatic ultrasound, sextant needle biopsies, histologic Gleason scoring, computed tomography, and magnetic resonance imaging currently provide the foundation for the clinical staging of prostate cancer.
If the disease is truly confined to the prostate, surgical removal of the gland should remove all traces of malignant cells. However, it has been shown that up to 40% of patients diagnosed preoperatively with prostate-confined disease using current modalities actually have disease outside the margins of surgical resection at surgery. (Lu-Yao, McIerran, Wasson, Wennberg. An assessment of radical prostatectomy. Time trends, geographic variation and outcomes. The Prostate Patent Outcome Research Team, JAMA 269:2633-2655 (1993); Voges, et al., Morphologic analysis of surgical margins with positive findings in prostatectomy for adenocarcinoma of the prostate, Cancer 69:520-526 (1992); Catalona et al., Nerve-sparing radical prostatectomy: extraprostatic tumor extension and preservation of erectile function, J. Urol. 134:1149-1151 (1985); Epstein, et al., Is tumor volume an independent predictor of progression following radical prostatectomy? A multivariate analysis of 185 clinical stage B adenocarcinoma of the prostate with 5 years of follow-up, J. Urol. 148:1478-1481 (1993)). This understaging of males exposes them to the morbidity of radical surgery without providing a cure.
An RT-PCR assay for PSA has been developed by Katz and co-workers which recognizes PSA-expressing cells. The RT-PCR assay uses PSA primers to detect prostate cells in the peripheral circulation prior to radical prostatectomy. (A. E. Katz, et al, Molecular Staging of prostate Cancer With the Use of an enhanced Reverse Transcriptase-PCR Assay, Urology 43:765-775 (1994)). This PSA assay detects only PSA antigens.
Another assay for detecting occult hematogenous micrometastatic prostatic cells is a modification of similar PCR assays uses PCR primers derived from the cDNA sequences of prostate-specific membrane (PSM) antigen. (R. S. Israeli, et al, Sensitive Nested Reverse Transcription Polymerase Chain Reaction Detection Of Circulating Prostatic Tumor Cells: Comparison Of Prostate-Specific Membrane Antigen And Prostate-Specific Antigen-Based Assays, Cancer Research 53:227-230 (1993)). This PSM assay detects only PSM antigens.
Even in view of these advances in prostate cancer cell detection, there still remains a need for better identification of prostate tumor antigens. In particular there is need for a single assay to detect the presence of both PSM and PSA antigens.